Research and Production Practice of SBRF-E Gold and Silver Refining New Process
I. Introduction China's accession to WTO, under the premise of gold to the market, in order to rapid development of enterprises, Shandong Zhaojin Gold Silver Refining Co., Ltd. in the original gold and silver refining technology, based on independent research and development of new SBRF-E gold and silver refining process. The production practice proves that the process has the advantages of strong adaptability, short production cycle, low production cost and stable product quality. Its various technical and economic indicators are at the international leading level, and the products produced can fully meet the needs of gold market transactions. Second, SBRF-E gold and silver refining process The SBRF-E gold refining process is shown in Figure 1. Figure 1 SBRF-E method gold and silver refining process (1) Gold refining process 1, coarse gold powder Shandong Zhaojin Gold and Silver Refining Co., Ltd. mainly uses crude gold as raw material for production. Before entering the SBRF-E refining operation, it first pulverizes the crude gold. The powdered powder has a particle size of -200 mesh of more than 95%. - The content of 120 mesh is greater than 99%. The whole process is pulverized into gold powder by flowing molten gold through a high-pressure spray water of 42 to 50 MPa. 2, pre-dip removal The crude gold contains impurities such as copper , lead , zinc and iron . If chlorination is directly carried out, these impurities will enter the chlorine immersion liquid and affect the quality of the reduced gold. Therefore, the crude gold needs to be pretreated. The prepreg process can selectively remove the base metal into an ionic state and enter the solution to remove it, thereby creating favorable conditions for improving the quality of the reduced gold powder. Pre-dip removal of miscellaneous hydrochloric acid as leaching agent, compressed air as oxidant, solid-liquid mass ratio S/L=1:4～1:5, reaction temperature 70-80°C, pH=0.5-0.7, the main chemical reaction occurs : Pb(Zn,Fe)+2HCl→Pb(Zn,Fe) Cl 2 +H 2 2Cu(Pb, Zn, Fe)+O 2 →2Cu(Pb, Zn, Fe)O Cu(Pb, Zn, Fe)O+2HCl→Cu(Pb, Zn, Fe)Cl 2 +H 2 O The gold content in the raw materials and the content of the impurity metals are also unstable due to the fluctuation of the properties of the gold raw materials. This requires technical conditions to adapt to changes in the chemical composition of these materials during the production process. The production practice shows that the technical conditions of SBRF-E pre-dip impurity process are easy to control, the production technical indicators are stable, the impurity removal effect is good, and the leaching rate of impurities such as copper, lead, zinc and iron is over 99%. The factors affecting the pre-dip removal effect are: the pH value of the leachate, the pre-dip reaction temperature, the solid-liquid ratio, the compressed air intake, and the pre-dip time. 3. Chlorination leaching gold The purpose of chlorination leaching gold is to convert the gold in the pre-dipped gold powder and the residual trace copper, lead, zinc, iron and other impurity metals into complex ions or ions into the solution, and make the potential similar to the gold electrode. The silver enters the slag as a solid precipitate. From the Au-H 2 O-Cl 2 system potential-pH diagram (see Figure 2) and some metal standard electrode potential meters (see Table 1), it can be seen that chlorine gas is introduced into the hydrochloric acid medium, and all metals are dissolved in hydrochloric acid. Among them, silver remains in the slag in the form of AgCl precipitation. Figure 2 Au-H 2 O-Cl 2 system potential-pH diagram at 25 ° C The main chemical reactions are: 2Au+2HCl+3Cl 2 →2HAuCl 4 2Ag+Cl 2 →2AgCl Pb(Zn,Fe)+2HCl→Pb(Zn,Fe)Cl 2 +H 2 ↑ H 2 +Cl 2 →2HCl Cu(Pb, Zn, Fe)+Cl 2 →Cu(Pb, Zn, Fe)Cl 2 2 Fe Cl 2 + Cl 2 → 2FeCl 3 Table 1 Standard electrode potentials for certain metals Me n+ /Me Fe 2+ /Fe Fe 3+ /Fe Cu 2+ / Cu Cu + / Cu Fe 3+ /Fe 2+ Ag + /Ag Pb 2+ /Pb Au 3+ /Au Au + /Au Standard electrode Potential / V -0.44 0.015 0.153 0.521 0.771 0.799 0.987 1.5 1.68 In order to ensure a high leaching rate, the choice of controlling the appropriate leaching conditions is the key to the process. (1) Hydrochloric acid concentration. In the chlorination leaching process, in addition to copper, lead, zinc, iron and other impurity metals into the solution, hydrochloric acid and chlorine also oxidize elemental gold to AuCl 4 - complex ions into the solution, the gold leaching rate with the concentration curve of hydrochloric acid see image 3. It can be seen from Fig. 3 that the gold leaching rate increases with the increase of the hydrochloric acid mass concentration, and the gold leaching rate can reach 99.99% when the hydrochloric acid mass concentration is greater than 200g/L. Figure 3 Effect of hydrochloric acid concentration on gold leaching rate (2) The amount of chlorine gas. When chlorine gas is introduced, gold, silver, etc. are oxidized, gold is transferred into the solution by AuCl 4 - complex ions, and silver is oxidized to form AgCl precipitate to separate gold from silver. As the chlorine consumption increased, the gold leaching rate increased. When the chlorine gas consumption exceeded 0.5 kg/kg Au , the gold leaching rate did not change significantly. The effect of chlorine gas consumption on gold leaching rate is shown in Figure 4. Figure 4 Effect of chlorine gas consumption on gold leaching rate (3) Solid-liquid mass ratio. Since the raw material contains less impurities, the solid-liquid ratio has little effect on the leaching of gold. Practice has proved that when the solid-liquid ratio S / L = 1: 3 ~ 1: 4, the gold leaching rate can reach 99.99%. (4) Leaching time. Chlorine gas reacts slowly with gold in the initial stage of chlorine leaching operation. The chlorine gas consumption is only a few cubic meters per hour, and the middle reaches 50m 3 /h. The reaction is intense and the leaching period is 2~3 m 3 /h. The curve of gold leaching rate with leaching time is shown in Fig. 5. Practice has shown that under normal circumstances, the chlorine leaching operation time is about 5h. Figure 5 Effect of leaching time on gold leaching rate (5) Reaction temperature. The effect of temperature on the gold leaching effect is very large. High temperature and high reaction rate, but the excessively high temperature of hydrochloric acid and chlorine volatilization in the solution will greatly reduce the leaching rate and increase AgCl and PbCl 2 The solubility in the solution, which affects the reduction of the next gold powder. According to the solubility of AgCl and PbCl 2 and the production practice, it is suitable that the chlorine immersion operation temperature is 85 ° C to 90 ° C. After the chlorine leaching operation, the solution must be cooled to 30 ° C ~ 40 ° C, so that AgCl, PbCl 2 precipitated, so as to effectively inhibit AgCl, PbCl 2 into the solution, to eliminate their contamination of the gold solution. 4, the restoration of gold After filtering and washing the chlorinated gold leaching solution, the pH value is adjusted to 0-0.5 with sodium hydroxide, and then the SBRF reducing agent is slowly added, and the AuCl 4 - is rapidly and thoroughly reduced by appropriately controlling the redox potential in the solution system. It is precipitated as a single gold, and other impurities are not reduced and remain in the poor liquid. At the end of one reduction, the potential is controlled at 690-700 mV, the gold reduction rate is 85%-90%, the gold powder quality is up to GB4134-94 No. 1 gold requirement; the secondary reduction potential is controlled above 390 mV, and the secondary reduction rate is 10% to 15%. The quality of gold powder is up to GB4134-94 No. 2 gold. In the production practice, the technical requirements for the gold reduction process are very strict. (1) Reducing agent dosage and reduction time. The reduction time is related to the SBRF reducing agent addition rate, and is generally controlled at about 3 hours in order to observe the reduction process and determine the reduction end point potential. The amount of SBRF reducing agent is 0.74kg/kg Au . After reduction, the mass concentration of poor liquid gold is less than 0.5mg/L. After the poor liquid is treated by sewage and the tail liquid is adsorbed by carbon, no atomic absorption spectrometer and ICP plasma spectrometer can detect the poor liquid. Contains gold. The effect of the amount of SBRF reducing agent on the gold reduction rate is shown in Figure 6. (2) Oxidation reduction potential. The effect of SBRF-E reduction of gold redox potential on gold reduction rate is shown in Fig. 7. It can be seen from Fig. 7 that the initial oxidation-reduction potential is controlled at 690-700 mV, the gold reduction rate is over 80%, and the control is between 390-400 mV, and the gold reduction rate is 100%. Figure 6 Effect of reducing agent dosage on gold reduction rate Figure 7 Curve of gold reduction rate with oxidation-reduction potential (3) Reaction temperature. SBRF is a reducing agent with very strong reducing ability, and temperature has little effect on the reduction rate of gold. However, if the temperature is too high, the gold powder is easy to form agglomerates, which is not conducive to cleaning and washing; when the temperature is too low, AgCl and PbCl 2 crystallize out, which is easy to cause gold powder pollution. Practice has shown that the optimum reduction temperature is 55 ° C ~ 57 ° C. (2) Silver refining process 1. Conversion of silver chloride The filter residue produced during the chlorination leaching process is mainly solid silver chloride, which is converted into crude silver by industrial iron powder: 2AgCl+Fe→2Ag+FeCl 2 Iron powder replacement is the primary battery reaction. The control conditions were m Ag : m Fe = 3.7 : 1, solid-liquid mass ratio S / L = 1: 10, pH < 1, and operating temperature of 60 ° C to 80 ° C. The silver replacement rate is 99.99%. The crude silver obtained by the replacement enters the silver electrolytic refining operation. 2, silver electrolytic refining Silver electrolysis is a relatively mature process, but this process uses high current density electrolysis to purify silver, which is rare in China. The process is highly efficient and the production cycle is short, only 18 to 20 hours. Electrolysis temperature 50 ° C ~ 65 ° C, electrolyte silver mass concentration 120 ~ 150g / L, pH = 2 ~ 3, cell voltage 5 ~ 6V, the same pole distance 140mm, current density 1000A / m 2 . The silver recovery rate is 99.99%. The product quality meets the standards of GB4135-94 No. 1 and No. 2 silver. Third, cost analysis According to the main materials, power and consumption in the past year, the production cost of gold and silver refining and the direct operation cost of silver electrolysis are shown in Table 2 and Table 3, respectively. Fourth, the conclusion 1. Production practice shows that the SBRF-E gold and silver refining process has a reasonable structure, short process, advanced technology and strong adaptability. 2. High degree of automation. The whole process uses the PLG automatic control system to control the process parameters, which greatly improves the labor intensity. 3. High recovery rate. The gold recovery rate is 99.96%, the silver recovery rate is 99.99%; the gold content in the discharged sewage is approximately 0, and the silver is less than 0.5 mg/L. 4. The product has high purity and stable quality, and the gold and silver products are in line with national quality standards. 5. The production cycle is short. The gold refining cycle is 36h, and the silver electrorefining cycle is 18 to 20h. 6. Low production costs. The production cost of gold is only 0.13 yuan / g, and the silver is 5.37 yuan / kg. 7. There is no process waste residue in the process; the wastewater is discharged to the standard; the negative pressure operation is used in the production process, and the extracted gas reaches the national emission standard after being sprayed and absorbed, and the production environment is excellent.
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